Central issue of my current research is physical oceanography of the east Asian marginal seas such as the Japan/East Sea or the East China Sea. Mysterious ocean variability will be uncovered by way of deductive numerical modeling and inductive data assimilation. I am also interested in atmosphere-ocean interaction and influence of the ocean circulation to fisheries.

Enhanced monitoring of ocean current using ADCP mounted in an international ferryboat crossing the Tsushima/Korea Strait

The primary purpose of the Collaboration is to conduct research toward 'Improvement of SST and predictability using NWP-ocean mixed layer coupled model'.

Numerical Experiment for Strontium-90 and Cesium-137 in the Japan Sea

The Coastal Ocean and Shelf Seas Task Team (COSSTT) deals with scientific issues in support of multidisciplinary analysis and forecasting of the coastal transition zone, as well as shelf/open ocean exchanges in relation with the larger-scale efforts.

MOON JAEHONG, Hirose Naoki, MORIMOTO Akihiko, Green's function approach for calibrating tides in a circulation model for the East Asian marginal seas, Journal of Oceanography, 10.1007/s10872-011-0097-1, 68, 2, 345-354, 2012.04, [URL], A simple effective method of inverse estimation provided by model Green's functions is examined to calibrate tides in a regional circulation model for the East Asian marginal seas. The Green's function optimization derived by perturbing the model parameters significantly improves the estimate relative to observation as compared with baseline integration. Among the optimized model parameters, the largest effects on cost function reduction come first from the harmonic constant of M 2 along the open boundaries with the optimized values of 89.7 ± 0.8% for amplitude, and second from the bottom friction with the optimized value of (3.06 ± 0.08) × 10 -3..

Jae Hong Moon, Naoki Hirose, Jong Hwan Yoon, Ig Chan Pang, Offshore detachment process of the low-salinity water around Changjiang Bank in the East China Sea, Journal of Physical Oceanography, 10.1175/2010JPO4167.1, 40, 5, 1035-1053, 2010.05, [URL], A patchlike structure of low-salinity water detached from the Chanjiang "Diluted Water" (CDW) is frequently observed in the East China Sea (ECS). In this study, the offshore detachment process of CDW into the ECS is examined using a three-dimensional numerical model. The model results show that low-salinity water is detached from the CDW plume by the intense tide-induced vertical mixing during the spring tide period when the tidal current becomes stronger. During the spring tide, thickness of the bottom mixed layer in the sloping bottom around Changjiang Bank reaches the mean water depth, implying that the stratification is completely destroyed in the entire water column. As a result, the offshore detachment of CDW occurs in the sloping side of the bank where the tidal energy dissipation is strong enough to overcome the buoyancy effect during this period. On the other hand, the surface stratification is retrieved during the neap tide period, because the tidal current becomes substantially weaker than that in the spring tide. Wind forcing over the ECS as well as tidal mixing is a critical factor for the detachment process because the surface wind primarily induces a northeastward CDW transport across the shelf region where tide-induced vertical mixing is strong. Moreover, the wind-enhanced cross-isobath transport of CDW causes a larger offshore low-salinity patch, indicating that the freshwater volume of the low-salinity patch closely depends on the wind magnitude..

Masaru Yamamoto, Naoki Hirose, Regional atmospheric simulation of monthly precipitation using high-resolution SST obtained from an ocean assimilation modelApplication to the wintertime Japan sea, Monthly Weather Review, 10.1175/2009MWR2488.1, 137, 7, 2164-2174, 2009.10, [URL], The present study examines the influence of an assimilation SST product on simulated monthly precipitation. The high-resolution SST structures located close to the oceanic front and coastal areas are important in regional atmospheric simulations over semienclosed marginal seas such as the Japan Sea. Two simulations are conducted using assimilation and interpolation SST products (experiments R and N, respectively), for January 2005. The surface heat fluxes and PBL height in experiment R are lower than those in experiment N in coastal areas and the cold tongue. A decrease of 4 K in SST leads to decreases of 120 W m-2 in surface sensible and latent fluxes and 300 m in PBL height. The precipitation in experiment R is less than that in experiment N for the sea area except at 38°N, 137°E. The cold tongue in the central Japan Sea acts to reduce moisture supply via the latent heat flux, resulting in low precipitation in coastal areas. The fact that the difference between observed and modeled precipitation in experiment R is 21% less than that in experiment N demonstrates that the assimilation of SST data leads to improved regional atmospheric simulations of monthly precipitation..

8.

Validation of the number of branches in the Tsushima Warm Current based on assimilated estimates, [URL].

9.

Jae Hong Moon, Naoki Hirose, Jong Hwan Yoon, Comparison of wind and tidal contributions to seasonal circulation of the Yellow Sea, Journal of Geophysical Research, 10.1029/2009JC005314., 114, 8, 2009.08, [URL], [1] Seasonal circulation of the Yellow Sea (YS) in response to wind and tidal forces is examined using a three-dimensional numerical model. Wind forcing affects the wintertime circulation of the YS; on the other hand, the summer southerly monsoon is weak and therefore has little impact on the circulation, on the basis of comparative experiments with and without wind conditions. Results indicate that the Yellow Sea Warm Current (YSWC) along the YS trough exists regardless of wind forcing. However, strong winter northerly winds intensify the southward coastal flows along both coasts of the YS, and therefore, the northward intrusion of the YSWC becomes stronger. These flows in the YS are substantially weakened when wind forcing is not applied to the model. In addition to wind-driven circulation, tide-induced circulation is also dominant in the YS, particularly in summer. In winter, the tidal effect weakens the upwind and downwind flows in response to the strong northerly winds, while in summer, tidal forcing induces a strong southward residual flow along the western slope and a cyclonic gyre with a bottom cold water dome at the central region of the YS. The southward residual current possibly explains the southward movement of the Yellow Sea Bottom Cold Water as observed in summer. Comparison to the effects of parameterized tidal mixing suggests that residual flow driven by explicit tidal forcing plays an important role in the summertime circulation of the YS..

10.

Naoki Hirose, Kazuya Nishimura, Masaru Yamamoto, Observational evidence of a warm ocean current preceding a winter teleconnection pattern in the northwestern Pacific, Geophysical Research Letters, 10.1029/2009GL037448, 36, 9, 2009.05, [URL], The role of the extratropical ocean in climate remains unclear due to the complexities in air-sea interaction processes. We have found robust evidence for the Tsushima Warm Current (TWC) preceding the western Pacific (WP) teleconnection pattern by conducting an analysis over the past 30 years. The WP index in winter sharply succeeds the volume transport of the TWC in autumn, but rather smoothly connects with the El Niño indices, indicating a considerable role of the ocean current in the climate system. Correlation patterns of seasonal precipitation over the Japanese Islands are also consistent with this relationship. The significant lead-lag correlations with the coherent structures of surface temperature indicate ocean-to-atmosphere feedback in which the interannual variation of the wind-driven current, represented by the TWC transport, influences the regional climate conditions associated with the WP pattern in winter..

11.

Naoki Hirose, Hideyuki Kawamura, Ho Jin Lee, Jong Hwan Yoon, Sequential forecasting of the surface and subsurface conditions in the Japan Sea, Journal of Oceanography, 10.1007/s10872-007-0042-5, 63, 3, 467-481, 2007.06, [URL], This study estimates a realistic change of the Japan Sea by assimilating satellite measurements into an eddy-resolving circulation model. Suboptimal but feasible assimilation schemes of approximate filtering and nudging play essential roles in the system. The sequential update of error covariance significantly outperforms the asymptotic covariance in the sequential assimilation due to the irregular sampling patterns from multiple altimeter satellites. The best estimates show an average rms difference of only 1.2°C from the radiometer data, and also explain about half of the sea level variance measured by the altimeter observation. The subsurface conditions associated with the mesoscale variabilities are also improved, especially in the Tsushima Warm Current region. It is demonstrated that the forecast limit strongly depends on variable, depth, and location..

12.

Numerical simulation of Kyucho along the eastern coast of the Noto Peninsula in 2004.

13.

Naoki Hirose, Ken ichi Fukudome, Monitoring the Tsushima warm current improves seasonal prediction of the regional snowfall, Scientific Online Letters on the Atmosphere, 10.2151/sola.2006-016, 2, 61-63, 2006.01, [URL], Seasonal predictions of rain or snowfall are usually too uncertain at regional scales. We suggest utilizing subsurface ocean measurements to improve long-term weather forecasts. The example we give is that regional snowfall in Japan can be predicted by a simple regression from an acoustic Doppler current profiler attached to a regular ferryboat to observe the transport of the Tsushima Warm Current. The lag correlation is shown to exceed 0.75 attributed to the simple underling marine meteorology and regional oceanography. The relationship certainly improves seasonal precipitation estimates led by the winter monsoon absorbing the latent heat from the Japan Sea. We predict there will be less snowfall this winter of 2005/2006 than in 2004/2005 despite the heavy snowfall event in the last December..

Naoki Hirose, Ichiro Fukumori, Victor Zlotnicki, Rui M. Ponte, Modeling the high-frequency barotropic response of the ocean to atmospheric disturbancesSensitivity to forcing, topography, and friction, Journal of Geophysical Research, 106, C12, 30987-30995, 2001.12, This study examines high-frequency sea level variations forced by changes in surface atmospheric pressure and wind and their sensitivity to different forcing mechanisms, bottom topography resolution, and amount of friction in a barotropic ocean model. Optimal model performance, defined in terms of the explained variance in satellite altimeter and bottom pressure data, is found when using relatively strong friction, equivalent to a damping timescale of only a few days over the deep ocean, and topography with minimal smoothing. Spatial variations of the optimal friction parameter seem to reflect the roughness of bottom topography. The model demonstrates skill in simulating the wind-driven response as well as the nonequilibrium response to atmospheric pressure variations..

17.

Naoki Hirose, Ichiro Fukumori, Rui M. Ponte, A non-isostatic global sea level response to barometric pressure near 5 days, Geophysical Research Letters, 10.1029/2001GL012907, 28, 12, 2441-2444, 2001.06, [URL], Changes in surface atmospheric pressure usually induce an isostatic response in the ocean characterized by an adjustment in sea level at the rate of approximately -1cm/hPa. Nonisostatic signals are, however, observed at many tropical tide gauges at periods near 5 days. Our analysis of satellite observations reveals the global nature of these signals, involving nonisostatic sea level fluctuations with nearly uniform phase within separate basins and an out-of-phase oscillation between the Atlantic and Pacific Oceans. Comparisons with a barotropic model further link the observed signals to forcing by a large scale pressure wave in the atmosphere and show that constrictions between basins prevent an isostatic response from being established. The apparent forced, nonresonant nature of the nonisostatic response contrasts with the predominantly resonant ocean dynamics at higher frequencies and may be relevant to explain the behavior of the long period tides..

18.

Naoki Hirose, Alexander G. Ostrovskii, Quasi-biennial variability in the Japan Sea, Journal of Geophysical Research, 105, C6, 14011-14027, 2000.06, [URL], The TOPEX/Poseidon (T/P) altimetry reveals quasi-biennial (QB) variability in the southern Japan Sea. Sea surface height anomalies of a biennial nature are most energetic in the Yamato Basin, the southeastern most part of the Japan Sea, where they can be as large as 20 cm and extend for 100-200 km. On the basis of the in situ measurements of Maizuru Marine Observatory, the 2-3 year variations are associated with thermohaline anomalies in the upper 300 m layer. The local QB oscillation is studied with a reduced gravity model of the Japan Sea. The model is forced by European Centre for Medium-Range Weather Forecasting daily wind and seasonal inflows/outflows through the three major straits of the sea. The model sensitivity experiments suggest that the QB variability can be associated with the sea's response to wind forcing of particular years, more specifically, 1992 and 1996, and to some extent, 1994. An approximate Kalman filter is employed for assimilation of the T/P altimeter data into the reduced gravity model. It filters out observational noise and intraseasonal sea level variability and allows the model to dynamically interpolate T/P observations. The results of the assimilation indicate that the QB anomalies are strongest at 37.5° N, 134.5° E and propagate west-northwest with a speed of ∼0.01 m s-1, contributing to variations of the Tsushima Warm Current..

19.

Naoki Hirose, Ichiro Fukumori, Jong Hwan Yoon, Assimilation of TOPEX/POSEIDON altimeter data with a reduced gravity model of the Japan Sea, Journal of Oceanography, 10.1023/A:1007707405711, 55, 1, 53-64, 1999.02, [URL], Sea level data measured by TOPEX/POSEIDON over the Japan Sea from 1993 to 1994 is analyzed by assimilation using an approximate Kalman filter with a 1.5 layer (reduced-gravity) shallow water model. The study aims to extract signals associated with the first baroclinic mode and to determine the extent of its significance. The assimilation dramatically improves the model south of the Polar Front where as much as 20 cm2 of the observed sea level variance can be accounted for. In comparison, little variability in the northern cold water region is found consistent with the model dynamics, possibly due to significant differences in stratification..

20.

Naoki Hirose, Hyun Chul Lee, Jong Hwan Yoon, Surface heat flux in the East China Sea and the Yellow Sea, Journal of Physical Oceanography, 10.1175/1520-0485(1999)029<0401:SHFITE>2.0.CO;2, 29, 3, 401-417, 1999.01, [URL], Climatological monthly mean variations of the surface heat fluxes over the East China Sea and the Yellow Sea are calculated by both a data analysis and a numerical simulation. The result of the data analysis based on the empirical/bulk method agrees well with the directly observed solar radiation and several previous studies of the surface heat fluxes. An adjustment in the formation of the Haney-type heat flux is presented by comparing to the result of the bulk method. The numerical simulation of these seas using an ocean general circulation model demonstrates the success of the improved Haney-type condition over the original one in simulating sea surface temperature. The surface heat flux simulated in the Yellow Sea is more reasonable than by the data analysis considering the total heat budget of this sea..

Naoki Hirose, Cheol Ho Kim, Jong Hwan Yoon, Heat budget in the Japan sea, Journal of Oceanography, 10.1007/BF02238321, 52, 5, 553-574, 1996.01, [URL], The long-term mean (31-year mean) surface heat fluxes over the Japan Sea are estimated by the bulk method using the most of the available vessel data with the resolution of 1° × 1°. The long-term annual mean net heat flux is about -53 W m-2 (negative sign means upward heat flux) with the annual range from 133 W m-2 in May to -296 W m-2 in December. The small gain of heat in the area near Vladivostok seems to indicate the existence of cold water flowing from the north. In that area in winter, the mean loss of heat attains about 200 W m-2, and the Bowen's ratio is over the unity. The largest insolation occurs in May in the Japan Sea, and the upward latent heat flux becomes the largest in November in this area. The heat flux of Haney type is also calculated, and the result shows that the constant Q1 has the remarkable seasonal and spatial variation, while the coefficient Q2 has relatively small variation throughout all seasons. Under the assumption of constant volume transport of 1.35 × 106 m3s-1 through the Tsugaru Strait, the long-term averages of the volume transport through the Tsushima and Soya Straits are estimated to be about 2.20 and 0.85 × 106 m3s-1 from the result of the mean surface heat flax, respectively..

The four-dimensional estimates of the Japan Sea circulation are provided for any of those who are interested in them. The data covers the entire Japan Sea (33-52N, 126.5-142.5E) for period from January 2nd, 1992 to November 19th, 2000 (total 3245days) with daily interval. The 1/6-degree, 19-level GFDL MOM (OGCM) was driven by daily ECMWF forecast and monthly inflow and outflow at the three openings. Satellite altimeter data of TOPEX/POSEIDON and ERS-1/2 were assimilated into the model by using approximate Kalman filter and RTS smoother. Please visit the URL:http://nmg.riam.kyushu-u.ac.jp/~nick/Assim/AMOM6/index.html.

Hirose, N., J.-H. Moon, and K. Takamine, Data Assimilation Research of the East Asian Marine System: Sensitivity Studies, Workshop on Marine Environment in the East China Sea and Its Sound Future, 2008.12.